The sensitivity of a receiver is generally limited by the presence of noise induced on the transmission medium from the signal transmitter, and also in the amplifier circuits of the receiver. The noise of the input stage of an opto-electronic receiver for an optical fiber link sets a limit on the range of the link. One of the known ways of guarding against noise is to protect the transmission medium as much as possible, using electronic components having low noise levels, and making use of a filter for eliminating frequencies in the, or each, band where there cannot be any signal (or where there is only a residual fraction thereof). Another technique consists in reducing the modulation rate of the encoded signal, thereby improving the signal-to-noise ratio but setting a limit on transmission performance. However, the noise present in the signal frequency band is not eliminated.
The present invention seeks to reduce noise, for example in order to increase the possible range of a link, in cases where the signal is an encoded signal transmitted at a fixed modulation frequency.